RADIATION DOSE-RESPONSE OF HUMAN TUMORS

Purpose: The dose of radiation that locally controls human tumors trea ted electively or for gross disease is rarely well defined, These dose s can be useful in understanding the dose requirements of novel therap ies featuring inhomogeneous dosimetry and in an adjuvant setting, The goal of this study was to compute the dose of radiation that locally c ontrols 50% (TCD50) of tumors in human subjects. Methods and Materials : Legit regression was used with data collected from single institutio ns or from combinations of local control data accumulated from several institutions treating the same disease. Results: 90 dose response cur ves were calculated; 62 of macroscopic tumor therapy, 28 of elective t herapy with surgery for primary control, The mean and median TCD50 for gross disease were 50.0 and 51.9 Gy, respectively, The mean and media n TCD50 for microscopic disease control were 39.3 and 37.9 Gy, respect ively, At the TCD50 an additional dose of 1 Gy controlled an additiona l 2.5 % (median) additional patients with macroscopic disease and 4.2% (median) additional patients with microscopic disease, For both macro -and microscopic disease, an increase of 1% of dose at the TCD50 incre ased control rates approximate to 1% (median) or 2-3% (mean), A predom inance of dose response curves had shallow slopes accounting for the d iscrepancy between mean and median values. Conclusion: Doses to contro l microscopic disease are approximately 12 Gy less than that required to control macroscopic disease, and are about 79 % of the dose require d to control macroscopic disease, The percentage increase in cures exp ected for a 1% increase in dose is similar for macroscopic and microsc opic disease, with a median value of approximate to 1%/% and a mean of approximate to 2.7%/%.